Zoom Ranges

The zoom range is a property of projected drawings and other components that appear in maps. Zoom ranges specify the zoom levels at which a component is displayed in a map, including the ability to "pin" the rendering of items to a given zoom level. For zoom levels outside the specified zoom range the component will automatically be hidden from view. The zoom range mechanism therefore makes it possible to create maps where dense components are not seen when the view is zoomed far out and where the component is displayed when zooming far enough into the map.

·Zoom ranges only affect the display of components within maps.

·Zoom ranges only work for projected components. They don't work for Latitude/Longitude unprojected components.

Zoom ranges are set within the native type of component window, but they become operational only when the component is displayed in a map window. Zoom ranges may be set by right-clicking on the layer's tab in a map window or by opening the layer in its own component window and then choosing View - Properties - Zooms.

To set zoom range, open the component in a window (for example, open a drawing in a drawing window) and choose View - Properties and then click on the […] button to the right of the Zooms caption to open the Zooms dialog.

The Zooms dialog offers these controls:

Minimum zoom

If blank, show component at any zoom level. If a value is entered, show component at any zoom level above this value and hide it otherwise.

Maximum zoom

If blank, show component at any zoom level. If a value is entered, show component at any zoom level below this value and hide it otherwise.

Render zoom

If blank, redraw points and labels at the same screen size regardless of zoom level. If a value is entered, render points and labels at their specified point sizes only at that zoom level and render points and labels at a larger size when zooming in beyond the specified render zoom level, and render them at a smaller size when zooming out from the specified render zoom level.

Current Zoom

The current zoom of the component when the View - Properties - Zooms dialog was launched. This provides a reference value from which we may get our bearings when deciding what values for zoom ranges or Render zoom we wish to use.

By default the Minimum Zoom and Maximum Zoom ranges are empty, which means the component will be visible in maps at any zoom level. We can choose preset zoom values in factors of ten from 1:1 to 1:1000000000 in the list boxes or we can enter a custom value. The Current zoom number shows the current zoom in the opened drawing window. It will vary as we zoom in or out of the window. It has no effect in setting zoom ranges except to provide a guide that may be used to estimate which zoom values to enter in the Minimum Zoom or Maximum Zoom boxes based on the current appearance of the component window.

If we set the Minimum Zoom range value set to 1:10000000 the component will not be visible at all zoom levels up to 1:10000000 after which it will be displayed in maps. If we zoom in to some zoom level below 1:10000000, say, to 1:100000, the component will not be displayed. As we zoom farther out to a zoom level above 1:10000000 the zoom level will appear.

If we like, we can enter a custom zoom range. For example, we can enter 30000000 in the Maximum Zoom box.

This setting of zoom ranges means that the component will be hidden in maps at zoom levels less than 1:10000000 as we zoom farther out and the zoom level goes above 1:10000000 the component will appear. If we continue zooming farther out beyond a zoom level of 1:30000000 the component will disappear. At all zooms between 1:10000000 and 1:30000000 the component will appear.

Very Important: Although the zoom range is set when the component window is open, it has an effect only when the component is displayed within maps. Also, zoom ranges can only be set on projected components. They cannot be set for components in Latitude / Longitude coordinates.

The default operation of Manifold within component and map windows is to provide a "dimensionless" rendering of point, line and area styles so that no matter what zoom is selected the styles will appear using the size specified in the format toolbar. For example, if a given point style is specified to be 6 printer's points in size, it will always be shown onscreen exactly 6 points in size. If we zoom in or out the point style will always be shown 6 points in size.

Manifold provides this behavior because vector components such as drawings can be zoomed in or out as much as we like. Normally when, say, many points are clustered together we would like them to continue to be the same size as we zoom further in so that many tightly bunched points can be resolved into visibly separate points.

In the default operation of Manifold, if we wish to have a "paper space" relationship between zooming in and out and the size of symbols such as points, we can use a print layout to create a composition based upon the fixed size of a sheet of paper. When we zoom in and out of a layout, the points and other vector symbols we see will get larger and smaller just as if we were looking at a printed sheet of paper more closely with a magnifying lens or from farther away.

In specialized applications we may want to force component windows to have the same behavior as a print layout display, where the size of labels, points and other symbols will change if we zoom in or out. We can force such behavior by specifying a Render zoom value. The Render zoom value specifies the scale at which styles will be drawn exactly at the size specified in the format toolbar. Zooming farther in, for lower zoom values, will cause the styles to be drawn proportionately larger in size. Zooming farther out, for higher zoom values, will cause the styles to be drawn proportionately smaller in size.

Inexperienced users are often confused between the free-scale world of vector component windows and map windows and the fixed-scale world of a print layout. The normal way of creating displays in which labels and symbols get larger and smaller as we zoom in or out is to use a print layout. Do not use the Render zoom parameter as a sloppy way to get a print layout effect within, say, a drawing or a map window just because the use of print layouts or scaling within print layouts is not understood. Better to study the documentation for print layouts and get those concepts clear so that the right tool may be used.

Keep in mind that one of the significant benefits of component windows like drawings and maps is exactly that they do not mimic the behavior of paper maps. For most purposes the default behavior of component windows provides benefits that would be obscured if symbols and labels were to get larger and smaller as we zoomed in. It is natural for beginners to want to approach GIS using the mental paradigms of paper maps, but it would be a mistake if such an approach denied users the signal benefits of a computerized workspace.

On the other hand, there are times when using a Render zoom value is the right choice. For example, suppose we want to publish a map component to the web using the Internet Map Server and to keep things conceptually simple for some users we want the resultant images to behave like a print layout when they are viewed. In that case, we can use Render zoom to make the image appear like a paper space image so that as visitors zoom farther into the image labels and point styles will appear larger.

Example

Consider a map of congressional districts in the US that includes as a layer a drawing containing points for major cities in the US.

We open the map and zoom in to whatever zoom we think will be our "standard" zoom, a typical view.

We then invoke View - Properties - Zooms and note the Current zoom value. It is approximately one to twenty six million.

We can enter 26000000 into the Render zoom box to make this the standard render zoom value.

If we now zoom farther into the drawing the point styles will increase in size. If we zoom twice as far into the drawing the points will be twice as large.

The farther we zoom into the drawing, the larger the point sizes will be, just as if we were viewing a printed sheet of paper through a magnifying lens.

Note that the display computed at the Render zoom value will be the same display, except for increase or decrease in size of symbols and labels, at higher or lower zooms. For example, zooming farther into the map does not allow any overlapping points to be resolved into separate points. This effect can be seen with labels.

Suppose we have a labels layer for the names of major cities in our map and we also set the Render zoom value for that labels layer to 1:26000000 just like the city points layer. Shown above is the map is zoomed to the same starting view, an approximately 1:26000000 zoom. The labels are displayed based upon computations for clipping overlapping labels at that zoom level.

As we zoom farther into the map, the labels simply get larger. No labels are added or deleted.

Just as the case with point styles, the farther we zoom into the map the proportionately larger the labels will become.

Comments

Why are zoom ranges not used in Latitude / Longitude maps? The reason is that such maps use geographic degrees as their unit of measure. Unlike meters or other linear measures used in projected coordinate systems, the size of a degree is different depending on its location on Earth. Degrees near the Equator are sixty nautical miles "wide" (their extent in longitude) but degrees very near the North Pole are only a few meters wide.

Because the size of a degree varies, any scale factor expressed in degrees also varies. If zoom ranges were allowed to apply in maps using Latitude / Longitude, one could have components appear and disappear in maps not as a result of zooming in or out but simply as a result of moving Northward or Southward along a particular meridian of longitude.